The present invention relates to a device for seismic exploration and specially designed for ice- and snow-covered regions, but also applicable on other surfaces on land or on the sea-bed.
Until now land-based prospecting techniques have been very labor intensive and time-consuming, and have not had the functional or economic efficiency which is at present available for marine seismic surveying.
Several suggestions have therefore been made for improvements of land-based seismic operations, for example the use of a towed main cable (streamer) to which subsidiary cables with automatically adjustable receiving instruments (geophones) are attached at suitable intervals. In order to use such towed systems on a solid surface it has until now been considered important that the cable system be able to withstand severe stresses and be so thick and strong that it can be towed within the area of operation. In snow- and ice-covered regions one has the additional risk that the cable may sink into the snow- and ice-cover and freeze therein, thus increasing the strength/stress requirements.
Such a streamer system designed for use on snow and ice surfaces is known from U.S. Pat. No. 3,954,154 to Kruppenbach et al. Furthermore, a method for mechanized land prospecting using such known streamer is known from U.S. Pat. No. 3,923,121 to Bendenbender et al. Such known streamer has a main cable composed of individual sections linked by means of connectors. A number of side strings with individual geophones are connected to the main cable with the geophones interconnected within the main cable. A tensile core consisting of seven steel wires is arranged in the central region of the cable in order to withstand a minimum force of eight tons (16,000 pounds). The steel core alone will thus have a diameter of at least 12 mm, and the resulting cable with surrounding rubber coating, conductor pairs, covering foils and outer mantle will weight several kilograms per meter and have a substantial diameter of 40-60 mm or more. A streamer using such a cable will be very heavy and can be stiff and unmanageable, similar to a heavy steel hawser, and is therefore not well suited for use in arctic regions. In addition, the steel wires will be acoustically active and possibly impair the signal quality. Such construction is therefore not suitable for full-scale commercial seismic operations, and in the above-mentioned patent no information is forthcoming on how the streamer concept has behaved in practical trials, or on results achieved.